Electrical biasing means



Oct. 17, 1944. w C EDDY ELECTRICAL BIASING MEANS Filed Feb. 28, 1941 INVENTOR, :1? c. EDDY W/L BY #5 A TTORN E Y.

Patented Oct. 17, 1944 ELECTRICAL BIASIN G MEANS William C. Eddy, Kenilworth, Ill., assignor to 'Radio Corporation of America, a corporation of Delaware Application February 28, 1941, Serial No. 381,143

8 Claims. '(Cl. 250-164) member comprises a Lucite rod having a key- My invention, in general, relates to television transmission apparatus and more particularly to apparatus for use with televsion transmission tubes such as Iconoscopes.

During the scanning of the photo-electric mosaic in an Iconoscope, in order to determine the light values impinging on the elemental areas thereof there are released a number of so-called secondary electrons, some of which travel sufiiciently far from the mosaic to be collected by variousoollecting means, and others are collected onto other sections of the mosaic itself due to the charge differentials on the various areas thereof, and hence this redistribution of secondary electron emission causes what is commonly called black spot or shading effects. Accordingly, it is one of the objects of my invention to substantially reduce or minimize socalled black spot effect in a television transmission tube.

It has been found that one of theways to minimize so-called black spot efiect is by casting or throwing or projecting a band of light around the border of the face of the mosaic and this not only distinctly lines the optical image to be transmitted, but also apparently effects the redistribution of secondary electrons within the inner sections of the mosaic so that shading or black spot is considerably lessened Accordingly,- it is another of the objects of my invention to provide a device which will cast a definite light bias around the border of an Iconoscope mosaic.

It has been found also that in an arrangement wherein a light bias is impressed upon a section of the mosaic around the border thereof, not only should the light be continuous around this section of the mosaic but should be substantially constant in value along all of the portions of the mosaic on which'the light is impressed, even though various sections of the mosaic may be at difiering distances from the source of light. Accordingly, it is another of the objects of my invention to provide an apparatus for impressing a light bias around a definite portion of the periphery or border of the mosaic in a television scanning tube, and in which the light is of substantially equal intensity along all portions thereof.

In general, my invention comprises providing a light conducting member which may be placed in the proximity of the mosaic, and from which a small beam of light emerges and is cast upon the border sections of the mosaic in a scanning tube. In one arrangement the light conducting way out therein of varying cross-sectional area in order to compensate for inequalities in the transmission of light from the source from'which the light is impressed onto the rod. The Lucite rod was then bent to embrace the outer periphery of the Iconoscope tube in such position as to allow the light to play around the border of the mosaic.

My invention will best be understood by reference to the drawing, in which:

Fig. 1 is a partially schematic showing of an embodiment of my invention.

Fig, 2 is a schematic view along a cutting plane .22 of Fig. 1.

Fig. 3 is a partial showing of an element of Fig. 1.

Referring to Fig. 1, there is shown an electronic scanning tube H), which in this instance is illustrated as an Iconoscope. This scanning tube may contain the normal electron gun structure as illustrated by the heating element ll, cathode l2, modulating electrode [3 and anode M. The tube also contains the norm-a1 photo-electric structure l5 onto which the optical image is projected to release electrons in accordance with the optical values of elemental portions of the image, and the mosaic is in turn scanned by the beam developed by the electron gun structure. For purposes of simplicity the deflecting means of the beam has not been shown nor has any focusing means been shown, nor has any particular type of second anode arrangement been shown, since these elements are not necessary to the purposes of the invention and to show the inventive concept. Embracing the outer periphery of the tube I0 is alight conducting rod 2%! whose general shape will be more clearly illustrated with reference to Fig. 2. Cut into the rod 20 is a keyway or slot 2| which may be of variable cross-sectional area or variable depth or variable width or a combination of variables of these parameters. One end of the rod passes through the covering ofa housing member 30 which may contain therein a plurality of lamp members, one of which is illustrated as 3|, and positioned behind the lamp member so as to throw the light onto the end of the light conducting rod is a reflecting member 33. For purposes of simplicity the energizing circuit of the lamps has not been shown. In actual experimental work the rod which is bent to embrace the outer periphery of the scanning tube comprises a Lucite or methyl methacrylate rod, but it will be appreciated that there may be many departures from the specific material illustrated without departing from the spirit and scope of the invention as, for instance, by using quartz.

Referring to Fig. 2, there is shown a view as seen on a cutting plane along the line 2-2 of Fig. 1. The Iconoscope I is illustrated with the photo-electric mosaic l5, and it will be seen that in this particular figure the rod member 20 is bent around the tube until it forms almost a closed circle. The ends of the rod then pass downwardly through the top of the housing 30 and one end is positioned adjacent the lamp member 3| with its associated reflector 33, whereas the other end of the rod is positioned adjacent the lamp 32 with its associated reflector 34. Again it will be appreciated that there may be departures from this particular showing because the arrangement seeks to light bias a strip along the edge of the mosaic and this strip is usually of equal width. At any rate the light flux per unit area is substantially constant. This strip is illustrated between the dotted line and the solid line forming the edge of the mosaic l and the two lines are indicated between the arrow members at the position 49. I'he slot 2| in the light conducting member is shown in the form of a dashed line in this figure.

Referring to Fig. 3, there is shown a portion of the methyl methacrylate rod for illustrative purposes. The slot 2! is illustrated and this figure shows that the slot may be of variable widths or variable depth or a combination of the two. It will be appreciated that since there must of necessity be some losses in the conduction of the light through the rod and further, since in a practical application of this idea the rod usually embraces the outer periphery of the tube, and that due to this latter feature the rod is not always equi-distant from the mosaic, some means must be provided to make the light emitted from a. particular section of the slot in one case greater than that of another particular section of the rod, and also the variable width or variable depth or variable total emitting surface can be used as a compensatory measure for the inequalities in light conduction along the rod.

I consider myself to be entitled to all departures from the specific showing of this invention which fall fairly within the spirit and scope thereof as defined in the hereinafter appended claims.

What I claim is:

1. Apparatus for applying a light bias to the border region of one of the substantially planar surfaces of a photoelectric member comprising a methyl methacrylate light conducting element positioned substantially to surround the periphery of said photo-electric member, and means for impressing light onto said methyl methacrylate member.

2. Apparatus for applying a light bias to the border region of one of the substantially planar surfaces of a photo-electric member comprising a quartz light conducting element positioned substantially to surround the periphery of said photo-electric member, and means for impressing light onto said quartz member.

3. An apparatus for applying a light bias to a photo-electric member comprising a rod-like light conducting element positioned adjacent said photo-electric member, said rod-like member having a slot cut into the surface thereof for at least a :portion of its length, said slot being of variable width, and means for impressing light onto said rod-like member.

4. An apparatus for applying a light bias to a photo-electric member comprising a rod-like light conducting element positioned adjacent said photo-electric member, said rod-like member having a. slot cut into the surface thereof for at least a portion of its length, said slot being of variable depth, and means for impressing light onto said rod-like member.

5. An apparatus for applying a light bias to a photo-electric member comprising a rod-like light conducting element positioned adjacent said photo-electric member, said rod-like member having a slot cut into the surface thereof for at least a portion of its length, said slot being of variable width and depth, and means for impressing light onto said rod-like member.

6. An apparatus for applying a light bias to the border region of one of the substantially. planar surfaces of a signal generating photo-electric mosaic member for the purpose of materially reducing a shading effect comprising a light conducting element positioned substantially to surround the pheri-phery of said signal generating photo-electric mosaic member, and means for impressing light onto the said light conducting element.

'7. An apparatus for applying a light bias to the border region of one of the substantially planar surfaces of a photo-electric member com prising a light conducting element positioned substantially to surround the periphery of said photo-electric member, said element having a slot cut along at least a portion of the periphery thereof, and means to supply light to the interior of said light conducting element.

8. Television apparatus comprising a scanning tube having a signal generating member providing a bi-dimensional light responsive surface included therein, a light conducting and transmitting member positioned to surround substantially the periphery of the said light responsive surface, and means for introducing light into the light conducting and transmitting member whereby a substantially constant intensity bias lighting is applied to the border areas of the said bi-dimensional surface for the purpose of materially reducing a shading effect.

WILLIAM C. EDDY. 

